This invention relates to a memory protection arrangement for use in a portable terminal device adapted for inventory control in a warehouse.
Conventionally, memory protection has been realized in various ways. One method is such that sum check data or the like is registered in a specified area of a memory when the memory is accidentally destroyed and the data is detected at ON/OFF timing for a power supply. With this method, therefore, abnormality can not be decided quickly in the event that a program becomes abnormal. In terms of hardware, this method is materialized as shown in FIG. 1 by including a controller 21 and a memory 22. The memory 22 is coupled to the controller 21 via a data bus 23 and an address bus 24 and controlled for reading by a memory read signal RD on line 25 and for writing by a memory write signal WT on line 26.
In another method, the 8-bit configuration generally used for memories is changed to a 9-bit configuration including one bit which is constantly used as a parity bit for checking. Disadvantageously, realization of all memories of a portable device with the 9-bit configuration is very costly and unpractical.
Generally, in many portable terminal devices, programs are stored in a ROM and inputted data is registered in a RAM. But, today, a RAM having a program which is down-loaded from a center apparatus has been used increasingly in many applications in order to smoothly comply with frequent change in specifications. This trend invites a problem that as soon as data in a RAM is destroyed by, for example, a noise, a program stored in the RAM immediately undergoes destruction and runaway.